Telephone transmitter



Zd. E. 55'

April 16, 1929. H. c. PYE

TELEPHONE TRANSMITTER Filed Deo. 10, 1925 Harn Patented Aprf 16, 1929.

HAROLD C. PYE, OF OAX PARK, ILLINOIS, ASSIGNOB T AUTOMATIC ELECTRIC INC.,

OF CHICAGO, ILLINOIS, A CORPORATION OF DELAWARE.

TELEPHONE TRANSMITTER.

Application led December `10, 1925. Serial No. 74,453.

This invention relates in general to telephone transmitters, more particularly to transmitters in which the microphone element is ofthe granular carbon type., and has for its principal object the development of a transmitter whose microphone cell will not open circuit or materially change in resistance regardless of the position in which the transmitter is used.

A further object of my invention is to provide a microphone cell of rugged construction without impairing its eiliciency.

Further objects of my invention will be apparent trom the detailed description and claims which follow..

Transmitters' used on desk telephones and cradle type telephone, more particularly on the latter type, are apt to be used in any position. That is, some people using the cradle au type telephone will hold the instrument in such a position that the main diaphragm ot the transmitter is horizontal with the micro phone cell beneath the diaphragm, that is, the

transmitter will be on its backa @ther people may hold the instrument in such a position that the microphone cell will be above the horizontal diaphragm, or, in other words, the transmitter will be on its tace,

lln the well known common battery type ot il@ telephone systems, either manually operated or automatically operated, the circuit ot a holding relay at the exchange entends through the transmitter at the substation and it this circuit is open the manual disconnect signal will be lighted, or the automatic switch train will be automatically released. ln the present well known type ot transmitter having parallel electrodes in the microphone cell, there is a strong probability that the transmitter will open circuit it it is laid on its lace or on its bach, or it the transmitter does not open circuit, it will increase in resistance sutilciently to allow this holding relay to restore with the above mentioned result, also the transmitter ot the well known type, because ot this increased resistance, is decidedly less emcient as a transmitting medium when it is operated with its electrodes in a horizontal position. llt is tor the correcting ot these tew very serious faults that ll have designed a transmitter built in accordance with the object of this invention tor use on a cradle type telephone.

'llhe drawings comprising lligs. l, 2, 3 and 4t show the details ot" a transmitter constructed dll in accordance with vthe object of'my invention. Figure 1 is a detailed crosssection View of a completely assembled transmitter shown 1n enlarged scale to permit a clear showing of the details. Figure 2 is a back view of the assembled transmitter showing particularly the back terminal mounting and insulation. Figure 3 is a detailed view ot the face of the back electrodes comprising electrode inembers 5 and 'l' separated by the insulating member 10. Fig. 4 shows the details of the connections between the electrodes and terminal strips.. A

Referring now to Fig. l in more detail, it will be noted that ll have assembled my transmitter in a standard trent piece l and on a standard baclr` bridge plate 2, these members not forming an essential part of the invention.. The microphone cell comprises the brass cup 3 into which l have mounted the electrodes 5, 6, l", and 8. lhe cell is com-I pletely lined with the insulating material 9, which may be et paper or any other suitable insulating material.,

'llhe microphone cell is fastened to the back bridge 2 by means ot the baclr electrodes 5 and 6, which entend through the cup, bridge and terminals, being insulated trom the cup and bridge by means ot the bushings 18 and lll, and. attached to the terminals l2 and 13 by means of the nuts l2 and i3". 'lhe mi crophone cell cup 3 is turther insulated trom the baclr ring by the insulating washer t7, and the terminals l?, and t3 are insulated trom this ring by means ot the common insulating mem er lil.

'llhe iront electrodes ll and tl are mounted on the mica diaphragm 22, which closes the granular carbon chamber, by means of the mounting member llt trom which the electrodes are insulated by the bushings 20 and 2l and the insulating washer 2l., Projecting trom this mounting member lt is the screw la' by means ot which the trent electrode assembly is attached to the main diaphragm 10o t by the lock nuts l5.. This liront electrode assembly comprising the mica diaphragm and electrodes is held on to the brass cup by means of the clamping ring 23, which may be either pressed on to the cup 3, or screwed on. I have placed a paper ring 23 between the clamping ring 23 and the mica diaphragm 22, to protect the latter trom injury as the former is being placed.

lThe main diaphragm is insulated from the 11o l, shown in Fig. 3. These electrodes comprise the, usual polished carbon face electrodes,

which are attached to the electrode stems and 7 by means of which the electrodes are With the transmitter used in the position shown in Fig. 1, the major path for the current is from the front electrode 8 to the back electrode 7, with a minor path through the electrodes 5 and 6. f

With the transmitter in such a position that the insulating members 10 and 11 are vertical there are two parallel aths through the granular carbon, the one rom the bottom part of electrodes 5 and 6 and the other from the bottom part of electrodes 7 and 8, the granular carbon being agitated by the movable electrodes'6 and'8 as before.

' Fi ure 2 shows the back view of the asattached to the microphone cell and bacl\semb ed transmitter disclosing a method I bridge as explained hereinbefore. The front electrodes 6 and 8 are constructed in a similar manner and are separated by the insulating members 11.

InA connecting'the four electrode members into the telephone circuit, I connect the back electrode 5 with the front electrode which is diagonally opposite, that is, the .electrode 8, and in a similar manner connect the electrodes 6 and 7 together. Byvthis arrangement I have secured a transmitter microphone cell which when lilled with granular carbon or other suitable comminuted resistance material, will not open circuit or materially increase in resistance in any position that it might be placed. The cell should be filled so that the carbon covers all electrodes when the transmitter is placed as shown.

Assume for the moment that the transmitter is being used while it is lying on its back, that is with the back electrodes 5 and 7 undermost. The supply of granular 'carbon in the microphone cell will then be resting squarely on these electrodes and will pile up touching parts of the front electrodes 6 and 8. The main path for the current in this case will be from the terminal 12 through the back electrode 5, through the granular carbon, through the back electrode7 and thence to the terminal 13 and out to the external circuit. The front electrode being vibrated by the main diaphragm in response to the voice waves directed against it, will alternately compress'and rarefy this granular carbon to change its resistance and modulate the electrical current in the well known manner. In this case the front electrodes 6 and 8 may carry some current as the granular carbon is also in contact with them, but the amount of this current and its ei'ect upon the external circuit is small.

In the event that the transmitter is being used face down, that is, with the front electrodes 6 and-8 undermost, the action is the same as that which has just been explained exce t that the major path for the current will e from the electrode 6 to the electrode 8, and that the entire pile of carbon will be moved by the vibrating front electrode assembly with the back electrode assembly as a stationary pusher.

employ to connect the diagonally opposite electrodes together. I have provided the terminal strips 12 and 13 which rest on the back bridge 2 and are insulated therefrom by means of the insulating strip 18. The screws of the back electrodes 5 and 7 extend through the back bridge and through these terminals being attached thereto by means of the nuts 12 and 13. In order to connect the diagonally opposite front electrodes to the 'terminal 12, I extend this terminal stri out and over the edfre of the back bridge 2 ending it down so that the soldering stri of the terminal lies adjacent to the nut hol ing the front electrode 8 to the front mounting plate 14. -I make a connection from this terminal to the nut by means of a flexible conductor. Similarly the terminal 13 is bent down and connected to the front electrode 6, thereby connecting the electrodes in pairs, 5 and 8, and 6 and 7.

Tests upon sample transmitters made substantially as shown in the foregoing description and drawings, show that the transmitters maintain a practically constant average resistance in all positions. In other words, these tests show that the spacing and size of the electrodes is such that the average resistance of the electrical path throu h the transmitter is the same, regardless of w iether that path is lateral between electrodes in the same plane or between electrodes in opposite planes. The tests also show a constant average resistance when the transmitter is .placed so that the path through it is made up of a combination of front to back paths and lateral paths. l

From the foregoing specification it is apparent that I have designed a new and useful transmitter structure, which will not open circuit or materiall change its resistance with a change in position, and which, because of its nearly constant resistance, has equally good transmitting quantities in all posltions. While I have chosen to show my invention in connection with a particular type of transmitter, I have done so merel by way of example, as there are man mo ifications which can be made by one Skil ed in the art without departing from the scope of my invention.

Having thus described my invention what I consider new and desire to have protected by Letters Patent is pointed out in the appended claims.

What is claimed'is:

1. In a telephone transmitter, a microphone cell having two back electrodes, said electrodes bein@ insulatedfrom said cell and from each other by suitable insulating members, a mica diaphragm closing said cell, a front electrode assembly on said diaphragm, said asscmbly` comprising two electrodes and a mounting member, said electrodes being insulated from said member and from each other by suitable insulators, terminals for said transmitter, one of said terminals being connected to one back electrode and to the iront electrode diagonally opposite, the other terminal being connected to the other backelectrode and to the front electrode diagonally opposite from it, granular carbon in said cell, and a path for current led into one of said terminals from an external circuit leading from the electrodes connected to that terminal, through said granular carbon to the electrodes connected to the other said terminal.

2. In a telephone transmitter, a microphone (cell, a plurality of rigidly mounted back electrodes, a plurality of movable front, electrodes, comminuted resistance material in said cell between said electrodes, means for connecting Vsaid electrodes in multiple to form a plurality of current paths through said resistance, some of said paths being between front and back electrodes and other paths being lateral between members of said front or bachl electrodes7 one or the other of said paths being the major path dependent upon the position'of the'transmitter, the'electrodes being so proportioned and spaced that the average resistance of said front and back major paths equals the average resist-ance of said lateral major paths.

, In witness whereof, I hereunto subscribe my name this 4th day of December, A. D.

HARoLDVc. PYE. 

